The await and async keywords were introduced in Dart 1.9.4 in order to simplify asynchronous operations. Consider the following call to a method that returns Future:

obj.method().then(handlerFunction)

This is fine for the post part, but what if things get more complicated and handlerFunction returns a future too?

obj.method().then(handlerFunction).then(handlerFunction2);

Things are starting to get complicated already—debugging is not straightforward. Ideally, we would want to deal with one part of the chain at a time and hold up the execution of statements until a desired operation is complete. This is what await allows:

var f1 = await obj.aMethod();
var result = await f1.aMethod();

Functions and methods to be called with await return Future. They must also be declared as async in the method's header, as does the function using the await call:

class Foo{
   Future<int> aMethod() async {
   return await aFunction();
  }
}

The async and await keywords...